Nowadays, LCD televisions have experienced great growth and are now rapidly gaining in popularity. As known, backlight modules are crucial components of LCD panels. In general, cold cathode fluorescent lamps (CCFLs) and light emitting diodes (LEDs) have been widely used as light sources of the backlight modules. Since a cold cathode fluorescent lamp uses a mercury gas, it is prone to environmental pollution. With maturity of the LED technology, LED gradually replaces CCFL as the backlight source of the LCD television. In comparison with CCFL, LED has reduced volume and power consumption. That is, the use of LED is effective for facilitating miniaturization of the LCD panel, achieving better color saturation and meeting the environmentally-friendly requirement.
Generally, a LCD panel comprises plural LED strings. Each LED string comprises a plurality of LEDs connected in series. As the size of the LCD panel is gradually increased, the number of LEDs included in each LED string of the backlight module is increased. In this situation, a high driving voltage generated by the driving circuit is necessary to drive all LED strings. In the backlight driving circuit of a conventional backlight module, a single positive driving voltage is used to drive a LED string. As such, the voltage difference between the heat-dissipating plate and each LED string is equal to the positive driving voltage. In other words, as the driving voltage is increased, the voltage difference between the heat-dissipating plate and each LED string is increased. For providing sufficient insulating efficacy, the insulating distance between the heat-dissipating plate and each LED string and the thickness of the insulating medium should be increased. As such, the high driving voltage fails to be transmitted to the heat-dissipating plate in order to prevent from burning out the LED backlight module.
Although the increase of the insulating distance and the insulating medium can enhance the insulating efficacy, there are still some drawbacks. For example, the increases of the overall thickness, volume and weight of the backlight module are detrimental to miniaturization of the backlight module and the LCD panel. Moreover, since the backlight module and the LCD panel become thicker, the heat generated by each LED string fails to be quickly conducted to the heat-dissipating plate. For enhancing the heat-dissipating efficacy, the dimension of the heat-dissipating plate needs to be further increased. In this situation, the overall thickness, volume and weight of the backlight module are further increased.
For reducing the insulating distance between the heat-dissipating plate and each LED string, the number of LEDs included in each LED string may be reduced. For example, in a case that the number of LEDs included in each LED string is decreased from 100 to 50, the driving voltage for driving each LED string may be reduced. Since the number of LEDs included in each LED string is decreased, the number of LED string is increased. In addition, the numbers of driving circuits and backlight connecting lines are increased, and thus the fabricating cost is increased. Due to the backlight connecting lines, the overall lateral distance is increased. Under this circumstance, the backlight module is not applicable to a rimless LCD television.
Therefore, there is a need of providing a LED backlight module and a backlight driving circuit so as to obviate the drawbacks encountered from the prior art.